The long-term objective of this laboratory is to determine why individuals with velopharyngeal inadequacy develop speech behaviors that tend to undermine speech performance. Recent studies in our laboratory suggest that these behaviors may be attempts to satisfy the requirements of a pressure regulating system. The specific aim of this research is to determine whether the compensatory responses associated with cleft and airway resistance. The purpose of a regulating systems is to maintain a parameter's constancy. The control process is the means by which this is accomplished. We propose that control of structural movements (resulting in upper airway resistance) and airflow is necessary for regulation of speech pressures. Study of a regulating system involves experiments which identify and describe mechanisms of control. The use of subjects with different degrees of velar inadequacy allows us to assess how the system responds when an error is introduced. Similarly, bite blocks and bleed valves will be used to assess the responses of normals to perturbations of a intact system. The pressure-flow technique will be used to measure respiratory parameters associated with speech and assess structural responses. The following questions will be addressed: 1. Does a loss of vocal tract resistance result in structural adjustments that maintain speech pressures? 2. Do structural adjustments for maintaining speech pressures undermine articulatory performance? 3. Does age affect the respiratory responses t a loss of vocal tract resistance? 4. Are changes in timing patterns associated with velopharyneal inadequacy consistent with the rules of a regulating system? 5. Does type of cleft affect respiratory, structural and articulatory responses? 6. What are the effects of auditory masking on responses to a loss of vocal tract resistance? 7. What parameter is being sensed by the detection system? If we determine that attempts to achieve aerodynamic constancy result in compensatory responses, then new explanations for cleft palate speech should follow and new approaches to treatment would be possible.